Method for slicing workpiece and wire saw

ABSTRACT

A method for slicing a workpiece using a wire saw which includes wire row formed by winding a fixed abrasive grain wire having abrasive grains secured to a surface around a plurality of grooved rollers, the method including feeding a columnar workpiece to wire row for slicing while allowing fixed abrasive grain wire to reciprocate and travel in an axial direction, thereby slicing the workpiece at a plurality of positions aligned in axial direction at same time. After end of slicing the workpiece, the fixed abrasive grain wire is rewound from position at the end of slicing the workpiece by length of ⅓ or more and ⅔ or less of the fixed abrasive grain wire fed&#39;s length from start of slicing when the workpiece and wire row begin to contact with each other to the end of slicing the workpiece, and then the workpiece is drawn out of wire row.

TECHNICAL FIELD

The present invention relates to a method for slicing a workpiece and awire saw.

BACKGROUND ART

As means for slicing off wafers from a workpiece such as a silicon ingotor a compound semiconductor ingot, wire saws have been conventionallyknown. In each of the wire saws, a wire row is formed by winding aslicing wire around a plurality of rollers in many turns, the slicingwire is driven in an axial direction at a high speed, and a workpiece isfed to the wire row for slicing while appropriately supplying slurry,whereby this workpiece is sliced at respective wire positions at thesame time (see, e.g., Patent Literature 1).

Here, FIG. 3 shows an outline of an example of a conventional generalwire saw. As shown in FIG. 3, this wire saw 101 is mainly constituted ofa wire 102 (a high tensile steel wire) to slice a workpiece W, a wirerow 104 formed by winding the wire 102 around a plurality of groovedrollers 103 and 103′, tension imparting mechanisms 105 and 105′ toimpart tension to the wire 102, a workpiece feed mechanism 106 whichfeeds the workpiece W to be sliced toward a lower side, and a slurrysupply mechanism 107 which supplies slurry having GC (silicon carbide)abrasive grains or the like dispersed in a liquid at the time ofslicing.

The wire 102 is reeled out from one wire reel 108, and reaches thegrooved roller 103 through the tension imparting mechanism 105. The wire102 is wound around this grooved roller 103 in approximately 300 to 400turns, and then taken up by the wire reel 108′ through the other tensionimparting mechanism 105′.

Further, the grooved roller 103 is a roller provided by press-fitting apolyurethane resin around a cylinder made of iron and steel and forminggrooves on a surface thereof at a fixed pitch. The grooved roller 103 isconfigured in such a manner that the wound wire 102 can be driven in areciprocating direction in a predetermined cycle by a driving motor 111.

It is to be noted that, at the time of slicing the workpiece W, theworkpiece W is held and pushed down by the workpiece feed mechanism 106,and fed to the wire row 104 wound around the grooved rollers 103 and103′. Such a wire saw 101 is used, appropriate tension is applied to thewire 102 by the tension imparting mechanism 105, the slurry fed from theslurry supply mechanism 107 is supplied through nozzles 109 whileallowing the wire 102 to travel in the reciprocating direction by thedriving motor 111, and the workpiece is fed for slicing by the workpiecefeed mechanism 106, thereby slicing the workpiece.

On the other hand, there is also known a method for slicing a workpieceby using a fixed abrasive grain wire having diamond abrasive grains orthe like secured to a surface of the wire in place of using slurrycontaining abrasive grains, and this has been partially put intopractical use for slicing of small-diameter ingots each having adiameter of approximately 150 mm or less.

In this slicing using the fixed abrasive grain wire, a general wire sawcan be used as it is by attaching the fixed abrasive grain wire in placeof the steel wire of the wire saw shown in FIG. 3 and changing theslurry to a coolant such as cooling water which does not containabrasive grains.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application PublicationNo. Hei 9-262826

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In slicing using the fixed abrasive grain wire, since loose abrasivegrains are not used, it has a merit that an amount of industrial wasteis small in environmental aspects. Further, it also has a merit that aprocessing rate is high, and has more conveniences than processing basedon the wire saw using the loose abrasive grains. However, in the wiresaw, as shown in FIG. 3, since the workpiece W is pressed against theone wire 102 wound around the grooved roller 103, moved, and sliced, theworkpiece W is placed at the end of slicing on a lower side of the wire103 against which the workpiece W was pressed. Thus, to take out theworkpiece W, the workpiece W must be moved up to allow the wire 102 topass through gaps between wafers sliced off from the workpiece W, andthe wire 102 must be relatively drawn out toward the lower side.

At the time of drawing out the wire, in case of the wire saw using theloose abrasive grains, since a gap (a clearance) corresponding to awidth of each loose abrasive grain G is formed between the wire 102 andthe workpiece W as shown in FIG. 4(a), extraction of the wire 102 isrelatively easy. However, as shown in FIG. 4(b), in case of the wire sawusing the fixed abrasive grains, since no gap is formed between thefixed abrasive grain wire 402 and the workpiece W, the fixed abrasivegrain wire 402 is hard to be drawn out. Thus, the fixed abrasive grainwire 402 is caught by the workpiece W and rises, trying drawing out thefixed abrasive grain wire 402 in this state causes damage to a workpiececut section, so-called saw marks are formed on this cut section, andWarp is degraded to impair quality. When the rise of the fixed abrasivegrain wire 402 has further increased, disconnection of the wire mayoccur. When the disconnection of the wire has occurred, an operation toagain wind the fixed abrasive grain wire around the grooved rollers isrequired, and great loss such as a need for an extra length of the fixedabrasive grain wire for rewinding is exhibited.

In view of the problem, it is an object of the present invention toprovide a method for slicing a workpiece and a wire saw which do notcause a wire to be caught by the workpiece and associated formation orsaw marks or disconnection of the wire in extraction of the wire afterslicing the workpiece.

Means for Solving Problem

To achieve the object, the present invention provides a method forslicing a workpiece with the use of a wire saw which includes a wire rowformed by winding a fixed abrasive grain wire having abrasive grainssecured to a surface thereof around a plurality of grooved rollers, themethod including feeding a columnar workpiece to the wire row forslicing while allowing the fixed abrasive grain wire to reciprocate andtravel in an axial direction, thereby slicing the workpiece at aplurality of positions aligned in the axial direction at the same time,the method being characterized in that, after end of slicing theworkpiece, the fixed abrasive grain wire is rewound from a position atthe end of slicing the workpiece by a length which is ⅓ or more and ⅔ orless of a length of the fixed abrasive grain wire fed from start ofslicing when the workpiece and the wire row begin to contact with eachother to the end of slicing the workpiece, and then the workpiece isdrawn out of the wire row.

In case of slicing the columnar workpiece, the abrasive grains securedto the wire surface have the greatest amount of abrasion in a workpiececentral portion due to a difference in slicing length, and the abrasionof the abrasive grains is reduced in any other portion. After the end ofslicing the workpiece, when the fixed abrasive grain wire is rewound bythe length falling within the range, a surface having a large amount ofabrasion of the abrasive grains secured thereto in the surface of thefixed abrasive grain wire can be arranged to be adjacent to theworkpiece, and the workpiece can be drawn out without being caught bythe wire. Consequently, it is possible to prevent the wire from beingcaught by the wire to form saw marks or prevent disconnection of thewire from occurring.

At this time, as the columnar workpiece, a workpiece having a diameterof 300 mm or more can be sliced.

The method for slicing a workpiece according to the present invention isparticularly effective when the columnar workpiece having a largediameter is sliced.

Further, to achieve the object, the present invention provides a wiresaw including: a wire row formed by winding a fixed abrasive grain wirehaving abrasive grains secured to a surface thereof around a pluralityof grooved rollers; and a workpiece feed mechanism which presses acolumnar workpiece against the wire row while holding the same, theworkpiece being sliced at a plurality of positions aligned in an axialposition at the same time by feeding the workpiece to the wire row forslicing while allowing the fixed abrasive grain wire to reciprocate andtravel in the axial direction, the wire saw being characterized in thatthe wire saw includes controlling means for controlling, after end ofslicing the workpiece, to rewind the fixed abrasive grain wire from aposition at the end of slicing the workpiece by a length which is ⅓ ormore and ⅔ or less of a length of the fixed abrasive grain wire fed fromstart of slicing when the workpiece and the wire row begin to contactwith each other to the end of slicing the workpiece, and then to drawthe workpiece out of the wire row.

Since the wire saw according to the present invention can be controlledto rewind the fixed abrasive grain wire by the length falling within therange after the end of slicing, a surface having a large amount ofabrasion of the abrasive grains secured thereto in the surface of thefixed abrasive grain wire can be arranged to be adjacent to theworkpiece, and then the workpiece can be drawn out. Consequently, it ispossible to prevent the wire from being caught by the wire to form sawmarks or prevent disconnection of the wire from occurring.

Effect of the Invention

According to the method for slicing a workpiece and the wire saw of thepresent invention, in extraction of the wire after the end of slicingthe workpiece, it is possible to prevent the wire from being caught bythe wire to form saw marks or prevent disconnection of the wire fromoccurring.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an example of a wire saw according tothe present invention;

FIG. 2(a) is a view showing a positional relationship between aworkpiece and a fixed abrasive grain wire after the end of slicing theworkpiece, (b) is a view showing a state of the workpiece and the fixedabrasive grain wire when a catch of the wire has occurred, and (c) is aview showing a positional relationship between the workpiece and thefixed abrasive grain wire after the end of drawing out the workpiece;

FIG. 3 is a schematic view showing an example of a conventional generalwire saw; and

FIG. 4(a) is a view showing a state of a wire in a gap of a workpiece ina loose abrasive grain system, and (b) is a view showing a state of afixed abrasive grain wire in a gap of a workpiece in a fixed abrasivegrain system.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be describedhereinafter, but the present invention is not restricted thereto.

In case of slicing a workpiece by using a fixed abrasive grain wire asdescribed above, there is a problem that, when drawing the wire out ofthe workpiece is tried after the end of slicing the workpiece, the wireis caught by the workpiece, saw marks are thereby formed on a section,or the wire is disconnected.

Thus, the present inventors have repeatedly conducted the earnestexamination to solve such a problem. Consequently, they have found outthat, when the fixed abrasive grain wire is rewound by an appropriatelength in such a manner that a surface of the fixed abrasive grain wirehaving a large amount of abrasion of abrasive grains secured theretobecomes adjacent to the workpiece, a diameter of the fixed abrasivegrain wire becomes smaller than a gap of the workpiece, and hence thewire can be prevented from being caught by the workpiece, therebybringing the present invention to completion.

FIG. 1 is a schematic view showing an example of a wire saw 1 accordingto the present invention. As shown in FIG. 1, the wire saw 1 accordingto the present invention is mainly constituted of a fixed abrasive grainwire 2 which is configured to slice a workpiece W and has abrasivegrains secured to a surface thereof, a plurality of grooved rollers 3and 3′ around which the fixed abrasive grain wire 2 is wound, a wire row4 formed by winding the fixed abrasive grain wire 2 around the groovedrollers 3 and 3′, a tension imparting mechanism 5 and 5′ configured toimpart tension to the fixed abrasive grain wire 2, a workpiece feedmechanism 6 which feeds the workpiece W to be sliced toward a lowerside, and a coolant supply mechanism 7 which supplies a coolant at thetime of slicing.

The fixed abrasive grain wire 2 is fed from one wire reel 8, passesthrough the tension imparting mechanism 5 formed of a powder clutch (alow-torque motor 10), a dancer roller (a deadweight) (not shown), or thelike via a traverser 9, and reaches the grooved roller 3. Furthermore,the fixed abrasive grain wire 2 is wound around the grooved rollers 3and 3′ in approximately 400 to 500 turns to enable forming the wire row4. Moreover, the fixed abrasive grain wire 2 passes through the othertension imparting mechanism 5′ formed of a powder clutch (a low-torquemotor 10′) or a dancer roller (a deadweight) (not shown) via a traverser9′ and is taken up by a wire reel 8′.

According to such a wire saw 1, when the workpiece W is fed to the wirerow 4 for slicing while allowing the fixed abrasive grain wire 2 toreciprocate and travel in its axial direction, the workpiece W is slicedat a plurality of positions aligned in the axial direction at the sametime. As to the reciprocatory traveling of the fixed abrasive grain wire2, the fixed abrasive grain wire 2 wound around the plurality of groovedrollers 3 and 3′ is advanced by a predetermined length in one directionand then retreated in the other direction by a length smaller than theadvancing amount, this is determined as one feed cycle, and the wire isfed out in one direction by repeating this cycle. The grooved roller 3′is configured to drive the fixed abrasive grain wire 2 wound therearoundin a reciprocating direction by using a driving motor 11 in apredetermined period.

Here, feeding and taking-up of the fixed abrasive grain wire will now bedescribed in more detail. FIGS. 2(a) and (c) are views each showing apositional relationship between the workpiece W and the fixed abrasivegrain wire 202 at the end of slicing the workpiece or at the end ofdrawing out the workpiece. As shown in FIG. 2(a), at the end of slicing,the workpiece W is placed on the lower side of the wire row. Thus, totake out the workpiece W, the wire 202 must be passed through the gapsbetween wafers of the workpiece, which has been sliced into the wafers,by moving up the workpiece W and relatively drawn out toward the lowerside.

However, in case of the wire saw using the conventional fixed abrasivegrain wire, since no clearance is formed between the fixed abrasivegrain wire 202 and the workpiece W (see FIG. 4(b)), the fixed abrasivegrain wire 202 is caught by the workpiece W and rises as shown in FIG.2(b), and saw marks are formed on a section of the workpiece W, ordisconnection of the wire occurs.

To avoid this problem, the wire saw 1 according to the present inventionincludes controlling means 12 which controls, after the end of slicingthe workpiece W, to draw the workpiece W out of the wire row 4 afterrewinding the fixed abrasive grain wire 2 from a position at the end ofslicing the workpiece W by a length which is ⅓ or more and ⅔ or less ofa length of the fixed abrasive grain wire 2 fed from the start ofslicing when the workpiece W and the wire row begin to contact with eachother to the end of slicing the workpiece W.

When the fixed abrasive grain wire 2 is rewound by a length which is ⅓or more and ⅔ or less of a length of the fixed abrasive grain wire 2 fedfrom the start of slicing to the end of slicing the workpiece W by usingits controlling means 12, a portion of the wire which has a large amountof abrasion of the abrasive grains can be arranged to be adjacent to theworkpiece, thereby preventing the workpiece from being caught by thewire to form saw marks at the time of drawing out the workpiece orpreventing the wire from being disconnected.

The method for slicing a workpiece according to the present inventionwill now be described based on an example where the wire saw of thepresent invention is used.

First, as shown in FIG. 1, the fixed abrasive grain wire 2 having theabrasive grains secured to the surface thereof is wound around theplurality of grooved rollers 3 and 3′ to form the wire row 4. Then, thefixed abrasive grain wire 2 is allowed to reciprocate and travel in theaxial direction of the fixed abrasive grain wire 2 by the driving motor11. Further, when the columnar workpiece W is fed to the wire column 4for slicing by the workpiece feed mechanism 6, the workpiece W is slicedat a plurality of positions aligned in the axial direction at the sametime.

According to the method for slicing a workpiece of the presentinvention, after the end of slicing the workpiece W, the fixed abrasivegrain wire 2 is rewound from a position at the time of the end ofslicing the workpiece W by a length which is ⅓ or more and ⅔ or less ofa length of the fixed abrasive grain wire 2 fed from the start ofslicing when the workpiece W and the wire row 4 begin to contact witheach other to the end of slicing the workpiece W, and then the workpieceW is drawn out of the wire row 4.

Consequently, when the workpiece W is drawn out, a surficial portion ofthe fixed abrasive grain wire 2 having a large amount of abrasion of theabrasive grains can be arranged to be adjacent to the workpiece W, andit is possible to prevent the fixed abrasive grain wire 2 from beingcaught by the workpiece W to form saw marks or prevent the wire frombeing disconnected at the time of drawing out the workpiece W.

Furthermore, it is preferable to slice the columnar workpiece having adiameter of 300 mm or more. As a size of the workpiece increases, alength of the fixed abrasive grain wire which is adjacent to theworkpiece and a distance to draw out the workpiece become longer, thefixed abrasive grain wire is apt to be caught, and hence the slicingmethod according to this application is particularly effective means.

EXAMPLES

The present invention will now be more specifically describedhereinafter with reference to examples and comparative examples of thepresent invention, but the present invention is not restricted thereto.

Examples 1 to 4

Such a wire saw of the present invention as shown in FIG. 1 was used toslice a columnar workpiece in accordance with the slicing method of thepresent invention, and the workpiece was drawn out of the a wire row. Asa fixed abrasive grain wire, one shown in the following Table 1 wasused.

TABLE 1 Core wire diameter 0.140 mm Diamond abrasive grain 10 to 20 μmWire outer diameter (nominal) 0.174 mm Abrasive grain fixing methodElectrodeposition of nickel

Moreover, workpiece slicing conditions and drawing conditions wereConditions 1 shown in the following Table 2. As described in Conditions1 in Table 2, a length of the fixed abrasive grain wire fed from thestart of slicing when the workpiece and the wire row begin to contactwith each other to the end of slicing the workpiece (this length will bereferred to as a wire used amount hereinafter) was set to 9000 m.

TABLE 2 Conditions 1 Conditions 2 Workpiece Diameter 301 mm 301 mmLength 300 mm 300 mm Wire traveling Wire tension 25 N 25 N conditionsWire traveling Up to 1500 m/min Up to 1500 m/min when workpiece rate issliced Wire advancing 2114 m 2128 m amount Wire retreating 2086 m 2072 mamount Wire used amount 9000 m 18000 m Workpiece feed Workpiece feed0.32 mm/min 0.32 m/min on conditions rate on average average whenworkpiece is sliced Wire traveling Wire tension 25 N 25 N conditionsWire traveling Up to 5 m/min Up to 5 m/min when drawing- rate out isWire advancing 1 m 1 m performed amount Wire retreating 1 m 1 m amountWorkpiece feed Workpiece feed 60 mm/min on 60 mm/min on conditions rateaverage average when drawing- out is performed Cooling water Liquid typeMixture of Mixture of water + water + glycol glycol Coolant flowApproximately Approximately rate 150 L/min 150 L/min Coolant 23° C. 23°C. temperature

Additionally, after the end of slicing the workpiece, the length ofrewinding the fixed abrasive grain wire was changed in Examples 1 to 4as shown in Table 3. As shown in Table 3, in Examples 1 to 4, the lengthof rewinding the fixed abrasive grain wire was set to be ⅓ or more and ⅔or less of the wire used amount. It is to be noted that, as theworkpiece, a columnar silicon single crystal ingot having a diameter of301 mm and a length of 300 mm was sliced.

TABLE 3 Presence/absence of Rewinding amount disconnection ComparativeExample 1   0 m Disconnected Comparative Example 2 1000 m DisconnectedComparative Example 3 2000 m Disconnected Example 1 3000 m Notdisconnected Example 2 4000 m Not disconnected Example 3 5000 m Notdisconnected Example 4 6000 m Not disconnected Comparative Example 47000 m Disconnected Comparative Example 5 8000 m DisconnectedComparative Example 6 9000 m Disconnected

In Examples 1 to 4 where the length of rewinding the fixed abrasivegrain wire was set to be ⅓ or more and ⅔ or less of the wire usedamount, presence/absence of disconnection of the fixed abrasive grainwire at the time of drawing the workpiece out of the wire row waschecked, and there was no occurrence of the disconnection.

Comparative Examples 1 to 6

As shown in Table 3, a columnar workpiece was sliced under the sameconditions as those in Example 1 except that a length of rewinding afixed abrasive grain wire after the end of slicing the workpiece was setto be less than ⅓ of a wire used amount or more than ⅔ of the wire usedamount, and the workpiece was drawn out of a wire row. It is to be notedthat, as shown in Table 3, in Comparative Example 1, the length ofrewinding the fixed abrasive grain wire after the end of slicing theworkpiece was set to 0 m, i.e., the fixed abrasive grain wire was notrewound after slicing.

Consequently, as shown in Table 3, the wire was disconnected in each ofComparative Examples 1 to 6 where the length of rewinding the fixedabrasive grain wire was set to be less than ⅓ of the wire used amount ormore than ⅔ of the wire used amount.

Examples 5 to 8

A workpiece was sliced and drawn out like Examples 1 to 4 except thatthe slicing conditions were changed to Conditions 2 in Table 2 and awire advancing amount and a wire retreating amount were changed to set awire used amount to 18000 m.

A rewinding amount of the fixed abrasive grain wire in each of Examples5 to 8 was set as shown in Table 4.

TABLE 4 Presence/absence of Rewinding amount disconnection ComparativeExample 7   0 m Disconnected Comparative Example 8  2000 m DisconnectedComparative Example 9  4000 m Disconnected Example 5  6000 m Notdisconnected Example 6  8000 m Not disconnected Example 7 10000 m Notdisconnected Example 8 12000 m Not disconnected Comparative Example 1014000 m Disconnected Comparative Example 11 16000 m DisconnectedComparative Example 12 18000 m Disconnected

Consequently, as can be understood from Table 4, in each of Examples 5to 8 where the length of rewinding the fixed abrasive grain wire was setto be ⅓ or more and ⅔ or less of the wire used amount, presence/absenceof disconnection of the fixed abrasive grain wire at the time of drawingthe workpiece out of the wire row was checked, and there was nooccurrence of the disconnection.

Comparative Examples 7 to 12

As shown in Table 4, a columnar workpiece was sliced under the sameconditions as those in Example 5 except that a length of rewinding afixed abrasive grain wire after the end of slicing the workpiece was setto be less than ⅓ of a wire used amount or more than ⅔ of the wire usedamount, and the workpiece was drawn out of a wire row.

Consequently, as shown in Table 4, the wire was disconnected in each ofComparative Examples 7 to 12 where the length of rewinding the fixedabrasive grain wire was set to be less than ⅓ of the wire used amount ormore than ⅔ of the wire used amount.

It is to be noted that the present invention is not restricted to theembodiment. The embodiment is an illustrative example, and any examplewhich has substantially the same structure and exerts the same functionsand effects as the technical concept described in claims of the presentinvention is included in the technical scope of the present invention.

The invention claimed is:
 1. A method for slicing a workpiece with theuse of a wire saw which comprises a wire row formed by winding a fixedabrasive grain wire having abrasive grains secured to a surface thereofaround a plurality of grooved rollers, the method comprising feeding acolumnar workpiece to the wire row for slicing while allowing the fixedabrasive grain wire to reciprocate and travel in an axial direction,thereby slicing the workpiece at a plurality of positions aligned in theaxial direction at the same time, wherein, after end of slicing theworkpiece, the fixed abrasive grain wire is rewound from a position atthe end of slicing the workpiece by a length which is ⅓ or more and ⅔ orless of a length of the fixed abrasive grain wire fed from start ofslicing when the workpiece and the wire row begin to contact with eachother to the end of slicing the workpiece, and then the workpiece isdrawn out of the wire row.
 2. The method for slicing a workpieceaccording to claim 1, wherein, as the columnar workpiece, a workpiecehaving a diameter of 300 mm or more is sliced.